Fig jam without added pectin will never set like a jelly. The aim is a jam that mounds on a spoon, holds a line drawn through it on a plate, and spreads without running off toast.
The cold plate test
Put two or three small plates in the freezer before you start. When the jam looks thick and the bubbles slow and become glossy, take the pan off the heat, drop a teaspoon of jam on a cold plate, and return it to the freezer for a minute. Push the edge with a fingertip. If the surface wrinkles and the jam holds a gap, it is done. If it floods back, cook a few minutes more and test again. Taking the pan off the heat while you test prevents overcooking.
The spoon test
Dip a cool metal spoon, lift it, and watch the jam fall. Early on it runs off in a stream; as it nears the set it falls in two drops that merge into a sheet.
Thermometer
A thermometer gives a number, and for a high-sugar jam that number is the standard setting point for your altitude. We treat it as a guide and confirm with the plate: fig jam can read done and still be looser than we want, or thicken more than expected as it cools.
Err on the soft side
Fig jam thickens further as it cools and over the first day in the jar. Jam that looks a shade loose in the pan is usually right; jam that looks perfect in the pan is often stiff in the jar.